Assay devices and methods

ABSTRACT

A device for determining an assay result may include a test strip, a light source system, a light detection system, and a processor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/615,723 filed Nov. 10, 2009, which is a continuation of U.S.application Ser. No. 11/773,325, filed Jul. 3, 2007, which is acontinuation of U.S. application Ser. No. 10/741,416, filed Dec. 19,2003, now U.S. Pat. No. 7,239,394, which claims the benefit of GBapplication Ser. No. 0312815.4, filed Jun. 4, 2003, and is also acontinuation of U.S. application Ser. No. 10/742,459, filed Dec. 19,2003, which claims the benefit of GB application Ser. No. 0312801.4,filed Jun. 4, 2003, and is also a continuation of U.S. application Ser.No. 10/816,216, filed Apr. 1, 2004, which claims the benefit of GBapplication Ser. No. 0312802.2, filed Jun. 4, 2003. Each of theaforementioned U.S. applications claims the benefit of U.S. ProvisionalPatent Application Ser. No. 60/508,001, filed Oct. 2, 2003. Each of theaforementioned U.S. and GB applications is hereby incorporated herein bythis reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of an assay resultreading device in accordance with the present disclosure.

FIG. 2 is a schematic representation of some of the components of theembodiment illustrated in FIG. 1.

FIG. 3 is a graph of typical results for reading (i.e. signal) againsttime.

FIGS. 4-6 are schematic representations of an embodiment incorporating apreferred light source/photodetector arrangement.

FIG. 7 is a plan view of certain internal components showing anembodiment of one arrangement.

FIG. 8 is an elevation view of certain internal components showing anembodiment of one arrangement and exemplary optical paths.

FIG. 9 is an exploded top perspective view of a baffle element and acircuit board of an exemplary embodiment.

FIG. 10 is a top plan view showing an exemplary baffle arrangement.

FIG. 11 is a bottom perspective view showing an exemplary bafflearrangement.

FIG. 12 is a bottom plan view showing an exemplary baffle arrangement.

FIG. 13 is an exploded cross-sectional side view taken at line 10-10 inFIG. 10 showing an exemplary baffle arrangement, circuit board, and atest strip.

FIG. 14 is a transverse cross-sectional view taken at line 11-11 in FIG.13 showing an exemplary baffle arrangement and a test strip.

FIGS. 15-17 are graphs showing various signals returned from differentportions of a test stick, inserted into the reading device illustratedin FIGS. 1-2, and their variation with time.

DETAILED DESCRIPTION

The present disclosure concerns, among other things, assay devices foruse with test strips.

For the avoidance of doubt, it is expressly stated that any of thefeatures described herein as “preferred”, “desirable”, convenient”,“advantageous” or the like may be adopted in an embodiment incombination with any other feature or features so-described, or may beadopted in isolation, unless the context dictates otherwise.

1. Early Determination of Assay Results

It is preferred, but by no means essential, that the assay is a lateralflow type assay, in which a liquid sample, possibly comprising theanalyte of interest, is applied to a liquid transport means (typicallycomprising a porous carrier, such as nitrocellulose) and migratestherealong. Assays of this type are well known to those skilled in theart and are disclosed, for example, in EP0291194.

The signal which accumulates during performance of the assay may beanything suitable for the purpose. Conveniently the signal accumulationcomprises formation or accumulation of a readily detectable substance(e.g. a coloured reaction product). More especially the assay preferablycomprises accumulation of a labelled reagent, typically deposition oraccumulation of the labelled reagent in the test zone or detection zoneof a lateral flow assay stick. The label may be, for instance, anenzyme, a radiolabel, a fluorochrome, a coloured particle or the like.In particular the assay conveniently involves the accumulation of aspecific binding reagent in the detection zone of a lateral flow assaystick, the specific binding reagent being labelled with a particle ofgold or a coloured polymer, such as latex.

Generally speaking, presence of the analyte of interest in the samplewill tend to cause accumulation of signal. However, in other formats(especially for example, competition or displacement formats), it is theabsence of the analyte of interest which may cause the accumulation ofthe relevant signal.

Again, generally speaking, in those embodiments of the device and methodof the present disclosure where presence of the analyte of interestleads to accumulation of the signal, the upper threshold value is setsuch that signal levels below this value are regarded as negative (i.e.the analyte is not present) and levels above are regarded as positive.

If after a certain period of time, the rate or amount of signalaccumulation has not reached the lower threshold limit, it is consideredthat the signal will never reach the upper threshold even if thereaction were allowed to proceed to completion, and an early negativeresult is then displayed. This would represent the case of a fluidsample having a very low analyte concentration.

Conversely, a result can be promptly displayed if the rate or amount ofsignal accumulation crosses the upper threshold limit. In the case of ahigh analyte concentration, the reading will cross the upper thresholdlimit at an earlier time and therefore an earlier than usual result maybe displayed.

In the intermediate case wherein the rate or amount of signalaccumulation crosses the lower threshold limit before a certain periodof time has elapsed but does not exceed the upper threshold, the readerwill wait until the reading crosses the upper threshold beforedisplaying a positive result. If the reading does not pass the upperthreshold before a further second period of time has elapsed, a negativeresult is displayed.

Thus the device is able to display the results as soon as convenientlypossible rather than necessarily wait for a preset time to elapse. Adevice in accordance with the present disclosure can therefore generallyindicate an assay result more quickly, especially where the analyteconcentration is very high or very low.

The reaction which leads to signal accumulation may be any suitablereaction e.g. a conventional chemical reaction between two chemicalentities, or an enzyme-catalysed reaction or reaction requiring someother catalyst, or may be a binding reaction. Preferred bindingreactions will involve the binding of at least one biological molecule.More especially, the reaction will preferably involve the binding ofmembers of a specific binding pair (“sbp”). Sbps are well known to thoseskilled in the art and include, inter alia, enzyme/substrate,antibody/antigen, and ligand/receptor pairs.

A preferred reaction involves the binding of a labelled analyte/reagentcomplex to specific binding reagent immobilised in a detection zone of alateral flow assay stick, the signal being accumulation of the label inthe detection zone.

The assay result reader will typically comprise an optical detectionsystem to detect accumulation of the label. Conveniently the readerdevice will comprise means of generating a signal (typically a digitalsignal) which is proportional to the amount of label accumulated.Desirably the optical detection system may measure an optical property,such as the amount of light reflected and/or transmitted from adetection zone in which the label accumulates. Suitable optical systemsare known to those skilled in the art and are disclosed, for example, inEP 0653625.

The preferred optical detection system will comprise at least one lightsource and at least one photodetector (such as a photodiode). Preferredlight sources are light emitting diodes or LED's. Reflected light and/ortransmitted light may be measured by the photodetector. For the purposesof this disclosure, reflected light is taken to mean that light from thelight source is reflected from the porous carrier or other liquidtransport means onto the photodetector. In this situation, the detectoris typically provided on the same side of the carrier as the lightsource. Transmitted light refers to light that passes through thecarrier and typically the detector is provided on the opposite side ofthe carrier to the light source. For the purposes of a reflectancemeasurement, the carrier may be provided with a backing such as a whitereflective MYLAR® plastic layer. Thus light from the light source willfall upon the carrier, some will be reflected from its surface and somewill penetrate into the carrier and be reflected at any depth up to andincluding the depth at which the reflective layer is provided. Thus, areflectance type of measurement may actually involve transmission oflight through at least some of the thickness of the porous carrier.

In a preferred embodiment the assay result reading device comprises ahousing formed from a light—impermeable material, conveniently asynthetic plastics material such as polycarbonate, ABS, polystyrene,high density polyethylene, or polypropylene or polystyrol containing asuitable light-blocking pigment.

The housing of the assay result reader typically comprises an aperturesuch that a test strip may be releasably inserted into and (preferably)engaged with the housing. The housing is designed such that ambientlight entering the interior of the reader is kept to an absoluteminimum. Desirably suitable alignment and fixing means are providedwithin the housing such that the test strip remains in a fixed positionwhen inserted. The light sources are arranged in the housing such that,when the test strip has been correctly inserted, they are correctlyaligned with the respective zone to be measured.

The assay test strip may be any conventional lateral flow assay teststrip such as those disclosed in EP291194 or U.S. Pat. No. 6,352,862.The test strip preferably comprises a porous carrier containing aparticulate labelled specific binding reagent and an unlabelled specificbinding reagent. The light sources and corresponding photodetectors arepreferably so aligned such that during use, light from the light sourcesfalls upon the respective zones on the porous carrier and is reflectedor transmitted to the respective photodetectors. The photodetectorsgenerate a current proportional to the amount of light falling upon itwhich is then fed through a resistor to generate a voltage. The amountof light reaching the photodetector depends upon the amount of colouredparticulate label present and therefore the amount of analyte. Thus theamount of analyte present in the sample may be determined. This methodof optically determining the analyte concentration is described morefully in EP653625.

In a typical embodiment, the assay result reading device will compriseone or more of the following: a central processing unit (CPU) ormicrocontroller; one or more LED's; one or more photodetectors; a powersource; and associated electrical circuitry. The power source may be abattery or any other suitable power source (e.g. a photovoltaic cell).

Conveniently the CPU or microcontroller will be programmed so asdetermine, from the output of the photodetectors, the rate or amount ofsignal accumulation and to compare this with the upper and lowerthreshold values.

In order to declare the assay result the reader will generally possesssome manner of indicating or communicating the result of the assay to auser. This may take the form, for example, of an audible or visiblesignal. Desirably the device will comprise a visual display to displaythe assay result. This may simply take the form of one or more LED's orother light sources, such that illumination of a particular light sourceor combination of light sources conveys the necessary information to theuser. Alternatively the device may be provided with an alphanumeric orother display, such as an LCD. In addition, or as an alternative, todisplaying the assay result, the device may also display or indicate insome other way to the user whether or not the result of the particularassay should be disregarded e.g. because a control result has failed. Ifthe reading device determines that a particular assay result should bedisregarded it may prompt the user to repeat the assay. Displayssuitable for displaying this sort of information are known to thoseskilled in the art and disclosed, for example, in WO 99/51989.

Advantageously the reader device will have some means of determiningelapsed time, such as an integral clock device.

Preferably the reading device is activated when an assay device isinserted into the reader device. This may be achieved by the userpressing a switch or button but, more preferably, is effectedautomatically, such that insertion of an assay device in the correctorientation and into the correct position within the reader causesactivation thereof. To facilitate this, it is preferred that the readerand the assay device are shaped and dimensioned so as to provide aprecise three dimensional fit. This concept is disclosed and describedin EP 0833145. In particular activation of the reader and/or insertionof an assay device into the reader may trigger the reader to commencetiming.

Desirably the reader is so programmed as to make a first determinationof the rate or amount of signal accumulation after a predetermined timeinterval. (Say, for example, 10 seconds after activation). If the rateor amount of signal accumulation exceeds the upper threshold or is belowthe lower threshold, and the control values (if any) are withinacceptable limits, the assay can be safely terminated and the results(positive, negative, or a semi-quantitative result) indicated to theuser. If however the determined rate or amount of signal accumulation isabove the lower threshold but below the upper threshold, the assay mustbe continued. The signal in this instance may be said to be anintermediate signal.

Typically there is an end-point, t_(e), at which the reader deviceconsiders the assay complete. If the signal is still below the upperthreshold value at t_(e) the result of the assay is negative (in thoseformats in which it is the presence of the analyte of interest whichleads to formation of the signal). The end-point of the assay may notnecessarily be at completion of the reaction. Indeed, the end-pointt_(e) will normally be considered to have been reached before thereaction is complete.

The t_(e) end point may conveniently be determined by the reader byreference to a particular time point (i.e. t_(e) may be considered tooccur a particular amount of time after commencement of the assay e.g. aparticular interval after activation of the reader and/or insertion ofan assay stick into the reader and/or application of the sample to thetest stick). For the purposes of illustration, t_(e) will typicallyoccur between 1 and 10 minutes, preferably between 1 and 5 minutes aftercommencement of the assay.

Desirably the assay result reader will be programmed so as to repeat thetest measurement if an intermediate signal is obtained. In a simpleembodiment the measurement is repeated at t_(e). Preferably however themeasurement is repeated one or more times before the end point. Mostpreferably the reader device is programmed to repeat the measurement atregular intervals (say, for instance 1 second or 5 second intervals)until the signal exceeds the upper threshold or until t_(e), which everoccurs first.

Inclusion of a clock or other timing device in the assay result readeris desirable so that the reader can automatically take measurements atpredetermined time points without further user input.

Thus, for example, the reader may be programmed to take measurements atan initial time point t_(o) and, if necessary to make repeatedmeasurements at any desired interval thereafter until the signal exceedsthe upper threshold or t_(e) is reached, as described above.

In addition, a clock or other timing device facilitates the readingdevice in determining the rate of signal accumulation. If measurementsof the amount of signal are taken at two or more time points (with aknown temporal separation), then the rate of signal accumulation mayreadily be calculated.

It should be noted that the rate or amount of signal accumulation couldbe measured either in absolute terms or as a relative valve (e.g.compared to a control or other comparison value, optionally obtainedfrom a substantially contemporaneous reaction).

2. Optical Arrangements

The optical arrangements for assay readers described herein promotesimplicity and economy. The manufacturing cost of the device is anespecially important consideration if the reader is intended to bedisposable; the photodetectors themselves, being relatively expensivecomponents, form a significant part of the overall cost.

A further advantage is that the arrangement can provide greater accuracyand reduce the need for accurate positioning of the test strip relativeto the reader. Suppose, for example, a test strip were provided with twoseparate, but closely spaced, control zones and a photodetector werepositioned in the reader so as to be between the two control zones. Ifthe test strip were slightly misaligned, laterally, relative to theassay reader device, the signal from one of the control zones would beless intense as the zone in question would be further from thephotodetector. However, the other control zone would necessarily becloser to the photodetector by a corresponding amount, and wouldtherefore provide a stronger signal to compensate for the weaker signalfrom the other zone. Furthermore it has been observed that the amount ofbound material present at a particular zone will vary along the lengthof the zone in the direction of liquid flow. Preferential binding of theanalyte takes place at the leading boundary edge and diminishes alongthe length of the zone in the direction of liquid flow. Thus anymisalignment may result in a greater error than might have been expectedif the analyte were captured in a uniform fashion. U.S. Pat. No.5,968,839 discloses an electronic assay reader for use with a teststrip, wherein it is attempted to compensate for this non-uniformbinding by the provision in the relevant binding zone of a plurality ofdeposits of immobilised capture reagent, the density of which depositsincreases from the leading boundary to the trailing edge of the zone.

Similarly, some of the arrangements described herein also reduce therequirement for precise relative positioning of the test strip and theassay result reading device: there is an in-built signal compensationfor any misalignment between the test strip and the assay result readerfor any zone which is commonly read by the two or more photodetectors,because relative movement of the commonly read zone away from one of thephotodetectors will necessarily (within certain limits) involve movementby a corresponding amount towards the other photodetector/s.

The light emanating from the zone or zones, as appropriate, may be lightwhich is reflected from the test strip or, in the case of a test stripwhich is transparent or translucent (especially when wet e.g. followingthe application of a liquid sample), light which is transmitted throughthe test strip. For the purposes of the present specification, lightincident upon a particular zone of a test strip from a light source, andreflected by the strip or transmitted therethrough, may be regarded as“emanating” from the strip, although of course the light actuallyoriginates from the light source.

The preferred light sources are light emitting diodes (LED's), and thepreferred photodetector is a photodiode.

Reflected light and/or transmitted light may be measured by thephotodetector. For the present purposes, reflected light is taken tomean that light from the light source is reflected from the test striponto the photodetector. In this situation, the detector is typicallyprovided on the same side of the test strip as the light source.Transmitted light refers to light that passes through the test strip andtypically the detector is provided on the opposite side of the teststrip to the light source. For the purposes of a reflectancemeasurement, the test strip may be provided with a backing such as awhite reflective MYLAR® plastic layer. Thus light from the light sourcewill fall upon the test strip, some will be reflected from its surfaceand some will penetrate into the test strip and be reflected at anydepth up to and including the depth at which the reflective layer isprovided. Thus, a reflectance type of measurement may actually involvetransmission of light through at least some of the thickness of the teststrip. Generally, measurement of reflected light is preferred.

It is especially preferred that the reading device of the second aspectcomprises a plurality of light sources, each light source being incidentupon a respective zone of the test strip.

In principle, an assay result reading device in accordance with thepresent disclosure may comprise any number of light sources and anynumber of photodetectors. For example, one embodiment includes threelight sources, each illuminating a respective zone of a test strip, anda single photodetector which is shared by all three zones. In practiceit is difficult to arrange for more than three zones to share a singlephotodetector, because the photodetector will have trouble in detectinga sufficiently strong signal from those zones which are furthest away.

In preferred embodiments, an assay result reader feature both “shared”photodetectors as well as “commonly read” zones; i.e., a singlephotodetector can receive light emanating from more than one zone, andlight emanating from a single zone is received by more than onephotodetector. In this instance, the reader will typically include aplurality of light sources and a smaller plurality of photodetectors. Inparticular, where the reader comprises x light sources for illuminatingthe test strip, it will comprise x−1 photodetectors. The number ofdetectors required might be reduced still further by sharing of thephotodetectors between the respective light sources, e.g. using threephotodetectors to detect light emanating from an assay test strip thathas been illuminated by five light sources.

More specifically, a preferred embodiment of an assay result readersincludes first, second and third light sources, each light sourceilluminating respective first, second or third zones of a test strip.Conveniently the first light source illuminates a test zone or detectionzone; the second light source illuminates a reference zone; and thethird light source illuminates a control zone. The test or detectionzone is a zone of the test strip in which an optical signal is formed(e.g. accumulation or deposition of a label, such as a particulatecoloured binding reagent) in the presence or absence, as appropriate, ofthe analyte of interest. (By way of explanation some assay formats, suchas displacement assays, may lead to the formation of signal in theabsence of the analyte of interest). The control zone is a zone of thetest strip in which an optical signal is formed irrespective of thepresence or absence of the analyte of interest to show that the test hasbeen correctly performed and/or that the binding reagents arefunctional. The reference zone is a zone wherein, typically, only“background” signal is formed which can be used, for example, tocalibrate the assay result reading device and/or to provide a backgroundsignal against which the test signal may be referenced.

In this particular preferred embodiment, the reader also includes twophotodetectors. The first photodetector is substantially adjacent to orprimarily associated with the first light source and is intended todetect light emanating the zone of the test strip illuminated by therespective light source. However, the photodetector is so positioned asto be also capable of detecting some of the light emanating from thesecond zone of the test strip, illuminated by the second light source.

The second photodetector is substantially adjacent to or primarilyassociated with the third light source and is intended to detect lightemanating from the zone of the test strip illuminated by the respectivelight source. However the photodetector is so positioned as to be alsocapable of detecting some of the light emanating from the second zone ofthe test strip, illuminated by the second light source.

Accordingly, this embodiment features a “shared” photodetector, becauseit includes a plurality of light sources and a photodetector whichdetects light emanating from at least two spatially separated zones ofthe test strip. In addition, this embodiment has “commonly read” zones,because it comprises two photodetectors, both of which are able todetect some of the light emanating from a zone of the test strip (inthis instance, two photodetectors are able to detect light emanatingfrom the second zone of the test strip).

It is preferred that, when the assay strip is correctly inserted into areader device, a commonly read zone will be at a position intermediatebetween the two photodetectors, such that (within certain limits) alateral movement away from one of the photodetectors will inevitablyinvolve a corresponding lateral movement towards the otherphotodetectors, so as to allow for the desired signal compensationeffect. Typically, but not essentially, the commonly read zone will beapproximately equidistant from the two photodetectors when the teststrip is correctly positioned within the reader.

It is also preferred that, where an assay result reading device includesa plurality of light sources, these are advantageously arranged suchthat a particular zone is illuminated only by a single one of theplurality of light sources. For example, optical baffles may be providedbetween or around the light sources so as to limit the portion of thetest strip illuminated by each light source.

3. Flow Rate Sensing

In describing the various embodiments, “fluid sample” refers to anyliquid material suspected of containing the analyte of interest. Suchsamples may include human, animal or man-made samples. Typically, thesample is an aqueous solution or biological fluid.

Examples of biological fluids include urine, blood, serum, plasma,saliva, interstitial fluid and so on. Other samples which can be usedinclude water, food products, soil extracts and the like for theperformance of industrial, environmental, or food production assays aswell as medical diagnostic assays. In addition, a solid materialsuspected of containing the analyte can be used as the test sample onceit is modified to form a liquid medium which may include furthertreatment in order to release the analyte.

Any suitable analyte or analytes of interest may be measured. Analytesthat are particularly of interest include proteins, haptens,immunoglobulins, hormones, polynucleotides, steroids, drugs, infectiousdisease agents (e.g. of bacterial or viral origin) such asStreptococcus, Neisseria and Chlamydia, drugs of abuse, and biologicalmarkers such as cardiac markers and so on.

Typically the disclosed assay result reading devices and methods areadapted to perform a diagnostic assay i.e. to provide information aboutthe health status of a mammalian (typically a human) individual subject.

It is preferred to calculate the rate of progress of the liquid sample(rather than the extent thereof) along the liquid transport carrier.

Conveniently the flow rate is calculated between two zones on the liquidtransport carrier, such that the presence of the liquid sample at, orpassage thereof through, a first, upstream zone is detected, andlikewise the present of the liquid sample at, or passage through, asecond, downstream zone is detected. If the distance between the twozones is fixed and/or known, the relative or absolute flow rate of theliquid sample can be readily calculated by measuring the amount of timewhich elapses between detection of the liquid sample at the first andsecond zones.

In principle, the first and second zones may be anywhere on the liquidtransport carrier so, for example, the first zone could be at theextreme upstream end and the second zone could at the extreme downstreamend. The distance between the two zones (and therefore the time travelof fluid sample) may be chosen to be any that is convenient and islikely to depend upon the nature of the analyte to be determined and thephysical dimensions and characteristics of the liquid transport carrier.For example the liquid transport carrier may comprise one or moremicrofluidic channels optionally containing one or more variousmicrofluidic elements such as a red-blood cell separation means,time-gates, or fluid rate controlling means, all of which will influencethe rate of travel of sample. In practice, it is desirable that the twozones are at a separation such that, at normal flow rates, asufficiently accurate flow rate may be calculated within the time frameof the assay, so as not to delay the assay process or assay resultdetermination. For an assay for the detection and/or quantification ofthe pregnancy hormone hCG, for example, a desirable time would bebetween 5 and 60 seconds.

Advantageously the presence of the liquid sample at, or passage through,one or more additional zones on the liquid transport carrier isdetected. This allows for a more accurate calculation of the flow rate.A larger number of flow rate calculation zones may be advantageous whenthe acceptable range of flow rates is rather narrow, or where the flowrate may vary at different portions of the liquid transport carrier(e.g. where there are portions with different flow characteristics, forinstance, due to the incorporation of microfluidic elements).

In addition the provision of a plurality of “check zones” allows forchecking that the liquid sample progresses through each of the zones inthe expected sequence, thereby alerting the user to an abnormal flowpattern if the liquid sample is detected at a downstream zone in advanceof detection at a particular upstream zone. Such abnormal flow patternscan occur for instance when a porous carrier is flooded by liquidsamples (“oversampling”).

If the calculated flow rate is outside of the predetermined acceptablelimits, then the result of the assay may be declared invalid. Thus theflow rate calculation can act as a control feature. If the calculatedflow rate is too high, due to flooding of the porous carrier (e.g. as aresult of oversampling; or a result of a faulty assay device due todefects in manufacture, or damage in storage or in use) the user can bealerted and the assay result disregarded. Equally, if the calculatedflow rate is too low (e.g. due to undersampling) the assay result can bedisregarded. Thus, errors due to, for example, over- or undersampling,may be avoided.

In principle any property of the liquid sample could be measured inorder to calculate the rate and/or extent of progress of the liquid,such as its electrical capacitance, conductivity or resistivity. Theporous carrier or other liquid transport carrier may comprise asubstance which undergoes a detectable change in the presence of theliquid sample. For example nitrocellulose, commonly used as a porouscarrier in lateral flow assay strips, is opaque (or substantially so)when dry, but its opacity is significantly reduced upon wetting. Thusmeasurement or detection of the change in optical reflectance ortransmissivity of a nitrocellulose carrier upon wetting by a liquidsample may be sufficient to detect the rate and/or extent of progress ofthe liquid sample.

Preferably the means for calculating the rate and/or extent of theprogress of the liquid sample applied to the liquid transport carriercomprises an optical detection system. Such an optical detection systemwill typically generate one or more signals (advantageously, electricalsignals) in a manner responsive to the rate and/or extent of theprogress of the liquid sample. In a preferred embodiment, a suitableoptical system comprises at least two light sources and at least onephotodetector, or conversely at least one light source and at least twophotodetectors, so as to be able to make optical measurements at leasttwo spatially separated zones of the liquid transport carrier.

In principle the light source could be external to the assay resultreader e.g. ambient light. However, this is extremely likely tointroduce variation, and it is therefore greatly preferred that: (a) theassay result reading device is provided with at least one integral lightsource (LED's are found especially convenient in this regard); and (b)the assay result reading device is provided with a housing or casingwhich substantially excludes, or at least greatly restricts, ambientlight from entering the interior of the reading device. For presentpurposes, a housing or casing will be considered to substantiallyexclude ambient light if less than 10%, preferably less than 5%, andmost preferably less than 1%, of the visible light incident upon theexterior of the device penetrates to the interior of the device. Alight-impermeable synthetic plastics material such as polycarbonate,ABS, polystyrene, polystyrol, high density polyethylene, orpolypropylene containing an appropriate light-blocking pigment is asuitable choice for use in fabrication of the housing. An aperture maybe provided on the exterior of the housing which communicates with theinterior space within the housing: a test strip or similar porouscarrier may be inserted through the aperture so as to perform an assay.

The liquid sample per se may have an optical property (e.g. colour)which renders it amenable to optical detection and/or monitoring of itsprogress along the liquid transport carrier. For example, a blood samplewill absorb strongly in the range 400 nm to 600 nm, due to the presenceof haemoglobin. Alternatively the liquid sample may be doped, prior toapplication to the liquid transport carrier, with a readily detectablesubstance (e.g. a dye, fluorochrome or the like) which will notinterfere with the performance of the assay but will facilitatedetection (especially optical detection) of the rate and/or extent ofthe progress of the liquid sample.

In yet another arrangement, the liquid transport carrier is providedwith a readily detectable substance which is transported by the liquidsample. Again, a dye, fluorochrome or the like may be suitable in thisregard. The readily detectable substance may conveniently be releasablyimmobilised on a porous carrier or the like, so as to be released uponcontact with the liquid sample. The readily detectable substance may bee.g. a coloured substance which does not interfere with the assay. In apreferred embodiment the readily detectable substance is a particulatelabel which is attached to a mobilizable specific binding reagent(having specific binding for the analyte), and detection of which labelin a detection zone constitutes an essential feature of the assay.

The particulate label may be anything suitable for the purpose,including coloured latex, a dye sol, or particulate gold. Alternativelythe particulate label may comprise a fluorophore which can be excited byan LED emitting radiation of a suitable wavelength.

The preferred optical detection system will comprise at least one lightsource and at least one photodetector (such as a photodiode). Preferredlight sources are light emitting diodes or LED's. Reflected light and/ortransmitted light may be measured by the photodetector. For the purposesof this disclosure, reflected light is taken to mean that light from thelight source is reflected from the porous carrier or other liquidtransport carrier onto the photodetector. In this situation, thedetector is typically provided on the same side of the carrier as thelight source. Transmitted light refers to light that passes through thecarrier and typically the detector is provided on the opposite side ofthe carrier to the light source. For the purposes of a reflectancemeasurement, the carrier may be provided with a backing such as a whitereflective MYLAR® plastic layer. Thus light from the light source willfall upon the carrier, some will be reflected from its surface and somewill penetrate into the carrier and be reflected at any depth up to andincluding the depth at which the reflective layer is provided. Thus, areflectance type of measurement may actually involve transmission oflight through at least some of the thickness of the porous carrier.

In one embodiment the reader comprises a housing in which is containedat least two light sources (e.g. LED's) and respective photodetectorsarranged to receive light from the LED's.

One of the light sources illuminates a first, upstream zone of theliquid transport carrier and another light source illuminates a second,downstream zone of the liquid transport carrier, and respectivephotodetectors are provided to detected light reflected and/ortransmitted from the respective zones, the amount of such light which isreflected and/or transmitted depending on whether the liquid sample(optionally together with any light-absorbing or light-emittingsubstance transported thereby) has reached the zone(s) in question.

In a particularly preferred embodiment the assay result reading devicecomprises three light sources which illuminate respective first, secondand third zones of the liquid transport carrier, and the flow rate ofthe liquid sample between at least two of the zones is measured.

Conveniently one of the zones from which measurements are made in thecalculation of the flow rate is also a zone from which measurements aremade in determining the result of the assay, for example, the first zonemay be a zone in which analyte-specific labelled binding reagent isimmobilised if analyte is present in the sample. Such a zone may bereferred to as a test zone.

Desirably one of the zones from which measurements are made in thecalculation of the flow rate is also a zone from which controlmeasurements are made for the purpose of obtaining a control value,which is used to determine if the assay has been correctly performed.Such a zone may be referred to as a control zone.

It is advantageous that there is a zone, from which measurements aremade in the calculation of the flow rate, which is also a zone fromwhich measurements are made in calibration of the assay result reader.Such a zone may be referred to as a reference zone.

It is desirable that the components of the assay reader used in thedetection and/or quantification of the analyte of interest are also usedin calculating the flow rate of the liquid. This confers advantages ofsimplicity and economy, which are especially desirable for a disposabledevice. In particular, a preferred assay result reader has an opticaldetection system for detecting the presence and/or amount of the analyteof interest, and the same optical detection system is employed to makemeasurements for the purpose of calculating flow rates.

In a particularly preferred embodiment the assay result reader obtainsmeasurements from a control zone, a reference zone and a test zone, thecontrol zone being downstream from the reference zone which is itselfdownstream of the test zone (i.e. the reference zone is between the testand control zones). The reference zone allows for, inter alia,measurement of an optical property (e.g. reflectance and/ortransmissivity) of the liquid transport carrier when wetted (e.g. awetted porous carrier). Conveniently results obtained from the test andcontrol zones are normalised relative to the reference zone, and thistakes into account and compensates for any variation in the opticalproperty of the sample. This is especially important when usingbiological samples, such as urine, which may vary widely in composition(e.g. concentration) and therefore vary in colour or colour intensity.

The housing of the assay result reader typically comprises an aperturesuch that a test strip may be releasably inserted into and (preferably)engaged with the housing. The housing is designed such that ambientlight reaching the interior of the reading device is kept to an absoluteminimum. Desirably suitable alignment and fixing means are providedwithin the housing such that the test strip remains in a fixed positionwhen inserted. The light sources are arranged in the housing such that,when the test strip has been correctly inserted, the light sources arecorrectly aligned with the respective zones to be measured.

The assay test strip may be any conventional lateral flow assay teststrip such as disclosed in EP291194 or U.S. Pat. No. 6,352,862. The teststrip preferably comprises a porous carrier containing a particulatelabelled specific binding reagent and an unlabelled specific bindingreagent. The light sources and corresponding photodetectors arepreferably so aligned such that during use, light from the light sourceor sources falls upon the respective zones on the porous carrier and isreflected or transmitted to the respective photodetectors. Thephotodetectors generate a current roughly proportional to the amount oflight falling upon it which is then fed through a resistor to generate avoltage. The amount of light reaching the photodetector depends upon theamount of coloured particulate label present and therefore the amount ofanalyte. Thus the amount of analyte present in the sample may bedetermined. This method of optically determining the analyteconcentration is described more fully in EP653625.

Alternatively, instead of using a test strip comprising a lateral flowporous carrier such as described by EP291194, a test strip having thebinding reagents disposed within a capillary could be used, such asdisclosed by U.S. Pat. No. 6,113,855.

In order to conduct an assay measurement using a assay result readingdevice in accordance with some of the preferred features, a test stripis inserted into the reader, and a liquid sample is then added to asample receiving portion of the test strip. Alternatively a liquidsample may be applied to the test strip first, and the strip theninserted into the reader. The sample migrates along the porous carrierand reaches a first zone, typically the test zone. When sample is addedto the strip, a coloured particulate label is resuspended and migratesalong the carrier along with the fluid. As the fluid front of the samplereaches first zone, there is a reduction in light intensity reaching thephotodetector since the coloured particulate label absorbs some of thelight. This change in reflected or transmitted light intensity isrecorded. In practice, a larger amount of the particulate label ispresent in the initial fluid front than in the subsequent fluid. Inaddition, if a binding reaction takes place in the test zone due to thepresence of analyte, particulate label will tend to remain in the testzone. Thus the shape of the resultant voltage-time profile observed willdepend upon whether the zone is a test, control or reference zone. For athree zone system, three voltage-time profiles will be recorded one foreach zone, having a time lag due to the fact that measurement zones arespatially separated from one another and thus the time taken for thefluid front to reach the first zone is less than that taken to reach thesecond and so on.

From analysis of the voltage-time profiles for the respective zones andwith knowledge of the distance between the zones, the rate of fluid flowmay be determined. By use of a simple algorithm, the final assay readingmay be rejected if the calculated flow rate has been determined to betoo low or too high.

In a typical embodiment, the assay result reading device will typicallyfurther comprise one or more of the following: a central processing unit(CPU) or microcontroller; two or more LED's; two or more photodiodes; apower source; and associated electrical circuitry. The power source maycomprise a battery or any other suitable power source (e.g. aphotovoltaic cell). The CPU will typically be programmed so as todetermine whether the calculated rate and/or extent of progress of theliquid sample is within predetermined limits.

Conveniently the assay result reading device will comprise some mannerof indicating the result of the assay to a user. This may take the form,for example, of an audible or visible signal. Desirably the device willcomprise a visual display to display the assay result. This may simplytake the form of one or more LED's or other light sources, such thatillumination of a particular light source or combination of lightsources conveys the necessary information to the user. Alternatively thedevice may be provided with an alphanumeric or other display, such as anLCD. In addition, or as an alternative, to displaying the assay result,the device may also display or indicate in some other way to the userwhether the calculated rate and/or extent of progress of the liquidsample is within the predetermined acceptable limits, and thus whetheror not the result of the particular assay should be disregarded. If thereading device determines that a particular assay result should bedisregarded it may prompt the user to repeat the assay. Displayssuitable for displaying this sort of information are known to thoseskilled in the art and disclosed, for example, in WO 99/51989.

EXAMPLES Example 1

An embodiment of an assay result reading device having both “shared”photodetectors and “commonly read” zones is illustrated in FIG. 1.

The reading device is about 12 cm long and about 2 cm wide and isgenerally finger or cigar-shaped. In preferred embodiments, the housingis no larger than about 12 cm long, about 2.5 cm wide, and about 2.2 cmtall. However, any convenient shape may be employed, such as a creditcard shaped reader. The device comprises a housing 2 formed from alight-impermeable synthetic plastics material (e.g. polycarbonate, ABS,polystyrene, high density polyethylene, or polypropylene or polystyrolcontaining an appropriate light-blocking pigment, such as carbon). Atone end of the reading device is a narrow slot or aperture 4 by which atest strip (not shown) can be inserted into the reader.

On its upper face the reader has two oval-shaped apertures. One apertureaccommodates the screen of a liquid crystal display 6 which displaysinformation to a user e.g. the results of an assay, in qualitative orquantitative terms. The other aperture accommodates an eject mechanismactuator 8 (in the form of a depressible button), which when actuated,forcibly ejects an inserted assay device from the assay reading device.

The test strip for use with the reading device is a generallyconventional lateral flow test stick e.g. of the sort disclosed in U.S.Pat. No. 6,156,271, U.S. Pat. No. 5,504,013, EP 728309, or EP 782707.The test strip and a surface or surfaces of the slot in the reader, intowhich the test strip is inserted, are so shaped and dimensioned that thetest strip can only be successfully inserted into the reader in theappropriate orientation. The assay device and a surface or surfaces ofthe slot in the reader, into which the assay device is inserted, mayalso be so shaped and dimensioned that there is a precise threedimensional alignment of the reader and an inserted assay device, whichensures that the assay result can be read correctly the reader.

When a test strip is correctly inserted into the reader, a switch isclosed which activates the reader from a “dormant” mode, which is thenormal state adopted by the reader, thereby reducing energy consumption.

Enclosed within the housing of the reader (and therefore not visible inFIG. 1) are a number of further components, illustrated schematically inFIG. 2.

Referring to FIG. 2, the reader comprises three LED's 10 a, b, and c.When a test strip is inserted into the reader, each LED 10 is alignedwith a respective zone of the test strip. LED 10 a is aligned with thetest zone, LED 10 b is aligned with the reference zone and LED 10 c isaligned with the control zone. Two photodiodes 12 detect light reflectedfrom the various zones and generate a current, the magnitude of which isproportional to the amount of light incident upon the photodiodes 12.The current is converted into a voltage, buffered by buffer 14 and fedinto an analogue to digital converter (ADC, 16). The resulting digitalsignal is read by microcontroller 18.

In some embodiments, a separate photodiode is provided to detect fromeach zone (i.e. the number of photodiodes equals the number of zonesfrom which reflected light measurements are made).

In other embodiments, such as that illustrated in FIG. 2, the number ofphotodetectors is less than the number of zones. One photodiode detectslight reflected from the test zone and some of the light reflected fromthe reference zone. The other photodiode 12 detects some of the lightreflected from the reference zone and the light reflected from thecontrol zone. The microcontroller 18 switches on the LED's 10 one at atime, so that only one of the three zones is illuminated at any giventime—in this way the signals generated by light reflected from therespective zones can be discriminated on a temporal basis.

FIG. 2 further shows, schematically, the switch 20 which is closed byinsertion of an assay device into the reader, and which activates themicrocontroller 18. Although not shown in FIG. 2, the device furthercomprises a power source (typically a button cell or two button cells),and an LCD device responsive to output from the microcontroller 18.

In use, a dry test strip (i.e. prior to contacting the sample) isinserted into the reader, this closes the switch 20 activating thereader device, which then performs an initial calibration. The intensityof light output from different LED's 10 is rarely identical. Similarly,the photodetectors 12 are unlikely to have identical sensitivities.Because such variation could affect the assay reading an initialcalibration is effected, in which the microcontroller adjusts the lengthof time that each of the three LED's is illuminated, so that themeasured signal from each of the three zones (test, reference andcontrol) is approximately equal and at a suitable operating position ina linear region of the response profile of the system (such that achange in intensity of light reflected from the various zones produces adirectly proportional change in signal).

After performing the initial calibration, the device performs a further,finer calibration. This involves taking a measurement (“calibrationvalue”) of reflected light intensity for each zone whilst the test stripis dry−subsequent measurements (“test values”) are normalised byreference to the calibration value for the respective zones (i.e.normalised value=test value/calibration value).

To conduct an assay, a sample receiving portion of the test strip iscontacted with the liquid sample. In this case of a urine sample forinstance, the sample receiving portion may be held in a urine stream, ora urine sample collected in a receptacle and the sample receivingportion briefly (about 5-10 seconds) immersed in the sample. Samplingmay be performed whilst the test strip is inserted in the reader or,less preferably, the strip can be briefly removed from the reader forsampling and then reintroduced into the reader.

Measurements of reflected light intensity from one or more (preferablyall three) of the zones are then commenced, typically after a specifictimed interval following insertion of the test strip into the reader.Desirably the measurements are taken at regular intervals (e.g. atbetween 1-10 second intervals, preferably at between 1-5 secondintervals). The measurements are made as a sequence of many readingsover short (10 milliseconds or less) periods of time, interleaved zoneby zone, thereby minimising any effects due to variation of ambientlight intensity which may penetrate into the interior of the readerhousing.

Example 2

FIG. 3 shows typical results for three different samples, in terms ofamount of signal (“Reading”, in arbitrary units) against time (inseconds).

The amount of signal is a measure of the light absorbed, or the decreasein light reflected, from the test zone of a lateral flow test stick asmight be determined using the assay result reader described in thepreceding example. In the presence of the analyte of interest, acoloured particulate labelled binding reagent accumulates in the testzone. The coloured particulate label absorbs some of the light incidentupon the test zone, and this reduces the amount of light reflectedtherefrom which is available for detection by a suitably positionedphotodetector. The higher the concentration of analyte, the more rapidthe rate of accumulation of label in the test zone and the stronger the“signal”.

Plot 1 illustrates a typical graph which might be obtained for a liquidsample which contains a high concentration of analyte. Plot 3illustrates a typical graph which might be obtained for a liquid samplewhich contains a very low concentration of analyte. Plot 2 illustrates atypical graph which might be obtained for a liquid sample which containsan intermediate concentration of analyte.

Also shown on the graph are two horizontal lines which indicate theupper threshold (“U”) and lower threshold (“L”) values respectively.

Referring to plot 1, the reader is programmed to make an initial readingat t(1), a certain predetermined length of time after commencement ofthe assay. The reading obtained is below the value of “U”, so an earlypositive result cannot be declared at t(1).

Equally, the reading is above the value of “L”, so an early negativeresult cannot be declared at t(1) either. In this situation, the readeris programmed to repeat the measurement after a further, predeterminedperiod of time has elapsed, at t(2). At t(2) the reading for plot 1 hasjust exceeded the value of U, so the reader can promptly indicate thatthe result is positive, via the LCD device.

Referring to plot 3, at t(1) the initial reading is below the value ofL, so the reader can promptly declare a negative result, since it can bepredicted that the value will never exceed the upper threshold beforethe predetermined end-point of the assay t_(e).

Referring to plot 2, the initial reading at time t(1) is, similar tothat for plot 1, below the value of U but above the value of L, so anearly positive or negative result cannot be declared. The same is trueat t(2). If desired, the reader can be programmed to make any number offurther readings at t(3), t(4) etc. until the final reading is taken att_(e). For plot 2, the final reading at t_(e) is still below the valueof U, so the assay result would be negative.

The following comments apply generally, not just to the exampledescribed immediately above. It should be noted that, rather thanmeasure absolute readings, values may be calculated with respect to therate of change of reading with respect to time, or d(reading)/d(time).Alternatively, the rate of change of slope with respect to time may bemeasured or d²(reading)/d(time)² or the integral ∫ d(reading) withrespect to two or more time values, namely the area defined by thecurve. This has the advantage that reading is averaged over time, whichsmooths any anomalies. Alternatively, the rate of change of slope withrespect to time may be measured or d²(reading)/d(time)². As a furtheralternative, all or some of the above measurements may be made incombination to yield a result. Thus rather than provide an early resultbased upon the value of the reading exceeding a lower or upperthreshold, the reader may make this evaluation based upon calculation ofa first or second differential, an integral or combination of one ormore thereof. Furthermore, an early result may be promptly declaredafter the reading has exceeded the lower threshold but the readerdetermines that the result will not exceed the upper threshold valuebefore the reading has reached equilibrium

Furthermore it may be noted that the values of the at least upper andlower threshold limits may be adjusted during the course of the assayreading. This may occur on the basis of the readings obtained earlier inthe course of the assay. It is preferable however that these valuesremain constant during the course of an individual assay.

As an alternative to promptly declaring the result, the reader may waitfor a certain defined period before declaring a result. This provides anextra control feature, such that for example a result is not declaredbefore various control checks have been made on either the assay strip,the reader or both. Such a situation might occur for a sample having anexceedingly high or low analyte concentration.

Example 3

An assay result reading device was created for making pregnancydeterminations based on the concentration of hCG in urine. The teststrip includes anti-hCG antibody coupled to a chromophore.

The upper threshold was set at 10% attenuation gain (AG) (signal vsreference), and the lower threshold was set at 6% attenuation gain(control vs ref). 10% AG corresponds to approximately 15 mIU hCG for anew test-strip and 25 mIU for an aged test-strip (aging is believed tocause decay of the antibody, resulting in an apparent increase ofsignal) and 6% AG corresponds to approx. 5 mIU. In other embodiments,the upper threshold can be set between about 10 and about 90% AG, andthe lower threshold between about 1% and about 9%, although in principleother value ranges could be chosen.

The initial time reference (t=0) is set when the control vs referencesignal passes through zero. This means that the sample fluid has reachedthe control line. The timer is then started. The analyte signal iscompared to the threshold values as described previously. The earliesttime point for a positive (pregnant) result is set at 20 seconds, andthe earliest point for a negative result is set at 60 seconds. In otherembodiments, of course, other time periods may be set.

The disclosed devices and methods may, naturally, be adapted for usewith a wide variety of analytes. In particular, it should be noted thatthe disclosed devices and methods may be used in situations in which anegative result is expected only in the absence of analyte, and also insituations where a negative result is appropriate even when the analyteis present in some amount. An example of the first situation is a testfor a pathogen, such as HIV or strep A. However, even in the absence ofanalyte, a lower threshold is still set and threshold test employed,because non-specific binding may otherwise result in a false-positivebackground reading.

An example of the second situation is an assay result reader forovulation that measures luteinizing hormone (LH), because LH is normallypresent at a basal level and surges shortly before ovulation; a positiveresult is desired during the surge, and a negative result during thebasal level.

Example 4

The above-described examples refer to assay result reading devices thatwork as one-time tests; i.e., a single test strip is assayed for asingle test result. The threshold values typically remain fixed fromtest to test for reliability and reproducibility.

However, some embodiments may employ a series of test strips in order totrack the amount of an analyte over time, and to adjust the thresholdvalues from strip to strip in the series order to provide preciseresults.

One example of such a system is an assay result reader that measuresluteinizing hormone (LH) over several days to predict ovulation based ondetecting the “LH surge” shortly before ovulation. In a typicalprocedure, a first measurement is made. If it is above a certain upperthreshold (for example, greater than 16% AG), a positive resultindicating “LH surge” is returned. If the measurement is below thisthreshold, then the upper threshold for the next test is adjusted,depending on the level measured. For example, if the signal is lowerthan 7% AG, the upper threshold is lowered to 13%. If the measurementfor the first test-strip is lower than respectively 5% or 3%, values ofrespectively 12% and 11% are chosen.

Thus, the algorithm chooses the threshold on the basis of the previousday's measurement, but it could also be an average of the previous daysmeasurements. Thus in general, the thresholds need not necessarily befixed.

Example 5

In some embodiments, the assay result reading device includes a memorysystem that stores prior test results accumulated over a period of time.For example, the device may be configured for testing for the presenceof a drug of abuse or a metabolite thereof, and the memory system canstore periodic test results. The device also includes a system forviewing or retrieving test results, such as by a display, and electronicconnection, or the like.

Example 6

In some embodiments, the assay result reading device includes a memorysystem that stores test profiles for a variety of analytes. A profilecan include, for example, the upper threshold and the lower threshold.The profile can further include time periods for performing thresholdcomparisons. In this manner, a single assay result reading device may beused to perform a variety of analyte assays.

The device further includes a selection system that selects theappropriate profile for the desired analyte. In some embodiments, theselection system can be a switch that a user sets to the desired test.In other embodiments, the selection system detects a feature on an assaytest strip indicative of the analyte to be measured. For example, thetest strip may have a bar code or other optical pattern. Alternatively,a test strip may be configured so that it remits light of a certainfrequency or in a frequency range that is characteristic for aparticular analyte. The memory system has a look-up table that theselection system may access to identify an analyte based on the remittedlight frequency.

Example 7

An assay result reader according to the present disclosure may alsoinclude a system for detecting flow rate of a fluid sample, such as onedescribed in U.S. patent application Ser. No. 10/742,459, filed Dec. 19,2003, attorney docket number ISA-007.01.

Example 8

An assay result reader according to the present disclosure may alsoinclude optical arrangement such as those described in U.S. PatentApplication Ser. No. 60/508,001, filed Oct. 2, 2003.

FIG. 4 is a schematic representation of the layout of the 3 LED/2Photodiode optical system described in Example 1. FIG. 5 is a schematicrepresentation of a side elevation of one LED/Photodiode, andillustrating their position relative to a nitrocellulose test strip.FIG. 6 is a schematic plan view of the LED/Photodiode arrangement, againillustrating their position relative to a test strip.

Referring to FIG. 4, an optics block component for accommodation withinan assay result reading device may include three LEDs (LED 1, 2 and 3)and two photodetectors (PD1 and PD2). Light from LED 1 illuminates atest zone of a test strip (not shown) inserted into the reader. Lightreflected from the test zone is detected by PD1. Light from LED3illuminates a control zone of the test strip and light reflectedtherefrom is detected by PD2. Light from LED2 illuminates a referencezone of the test strip.

Each LED is optically isolated by light-impermeable baffles 40, whichensure that the various LEDs are capable of illuminating only itsrespective zone of the test strip. However the surfaces of the bafflesfacing LED2 are angled so as to allow LED2 to illuminate a slightlywider portion of the test strip than LED1 or 3, and this in turn allowslight reflected from the reference zone to be detected by both PD1 andPD2.

The relative positioning of the test strip, LEDs and photodiodes may bebetter understood by reference to FIGS. 5 and 6.

Referring to FIG. 5, a test strip 20 is inserted into the reading deviceabove the plane of the LEDs and photodiodes. The test strip 20 is oflaminate construction including an uppermost backing layer 22 ofreflective opaque white MYLAR®, a synthetic plastics material, and alowermost front layer 24 of clear MYLAR®. Sandwiched between the MYLAR®layers 22, 24 is a layer of porous material 26 (typicallynitrocellulose). The purpose of the MYLAR® layers is to protect thedelicate nitrocellulose and provide mechanical strength and rigidity. Inaddition, the opaque backing layer 22 is relatively highly reflective,and this serves to improve contrast: relatively little light is absorbedby the layers 24, 26 and much of the light incident upon the variouszones would therefore tend to pass straight through the test strip, butthe reflective MYLAR® backing layer 22 ensures that this light isreflected. In addition, since the particulate label accumulating in thenitrocellulose layer 26 absorbs only a portion of the light as it passesthrough in a generally upwards direction, the label has in effect asecond chance to absorb light as it passes back through the test strip20 in a generally downwards direction, having been reflected by theopaque MYLAR® backing layer 22. This significantly improves thesignal-to-noise ratio.

As can be seen from FIGS. 5 and 6, the photodiodes PD1 and PD2 arealigned with their respective LEDs, LED1 and 3, but are offset, in thatthe LEDs lie towards one side of the test strip while the photodiodeslie towards the other side. Having the photodiodes offset in this wayavoids, or at least reduces, the amount of specular reflection from theclear MYLAR® layer 24 detected by the photodiodes (i.e. light which isreflected directly from the initial MYLAR® layer 24 without everpenetrating into the nitrocellulose layer—detection of such reflectionswould decrease the signal:noise ratio).

Referring to FIG. 5 the relationship between signal intensity (I) andthe angle (θ) of the reflected light relative to the photodiode is I∝cos θ⁴. Furthermore, the relationship between signal intensity (I) andthe distance (x) of the photodiode from the reflecting object is I∝1/x²(i.e. the inverse square law). It is apparent that, in view of theinverse square law, it would generally be preferred to position thephotodiodes as close as possible to the test strip (i.e. decrease x), soas to increase the signal intensity I. However, merely decreasing thevertical separation y between the photodiode and the test strip wouldincrease angle θ, decreasing the value of cos θ and therefore tend toreduce the signal intensity.

An alternative approach to improve signal intensity would be tore-position the photodiode nearer the center of the system (indicated bythe dotted lines in FIG. 5) which would simultaneously decrease x and θ.However, this is found to be undesirable as it increases the likelihoodof detecting specular reflections. Accordingly an aligned but offsetposition for the photodiodes provides an optimal compromise of theconsiderations.

It may be noted from FIG. 6 that photodiode 1 is aligned with the testzone and photodiode 2 is aligned with the control zone. This alignmentensures that any variation of the relative positioning of the test stripand assay reader has minimal effect on the angle θ. While PD1 and PD2are not aligned with the reference zone, and are therefore subject to arelatively large (and therefore undesirable) angle of θ, this problem isnot significant because (i) the use of two detectors to read thereference zone allows for compensation of any positional variation,since relative movement of the test strip so as to increase 8 for onephotodetector may decrease θ for the other photodetector; and (ii) thereference zone is used to give a background reading for calibrationpurposes—the photodiodes are not required to measure the signalintensity from a narrow line (as with the test or control zones), and sothe measurement of the reference zone signal is inherently lesssensitive to variation from mis-positioning.

Example 9

This example described in greater detail the features of the preferredarrangement of LED's and photodiodes outlined in Example 1.

FIG. 7 shows a plan view of an exemplary embodiment of an opticalarrangement. In this embodiment, the optical arrangement include threelight emitting diodes and two photodetectors. The active area (A) of thephotodetectors (PD) is 1.5 mm×1.5 mm. The optics are arranged such thatcenter lines of LED's 1 and 3 correspond to the center lines of PD 1 andPD2. The 3 LED's and two photodetectors are disposed within an area nolarger than about 1 square cm, preferably no larger than about 0.7square cm, specifically 1 cm×0.7 cm.

Also shown is the position of the test-strip 30 that is positioned abovethe LED's. The test-strip is inserted so that the test and control lines32 are situated above respectively LED's 1 and 3. The distance D, namelythe distance between the PD and LED, is preferably large enough toprevent specular reflection of light emitted from the LED from thesurface of the test-strip directly to the PD. This distance will bedependent upon various factors such as the size of the windows, as wellas the distance between the windows and the LED's and will be bestdetermined by routine experimentation. The windows are situated abovethe respective LED's that effectively define the areas through whichlight shines. In one exemplary embodiment, the dimensions of the windoware 2 mm wide by 2.75 mm high.

FIG. 8 shows the spatial relationship between the LED and photodiode.The photodiode is positioned at a sufficient distance to ensure that itdoes not receive specular reflections from the front cover of thetest-strip 30. Specular reflections are a direct reflection. Thus anylight hitting the test-strip at an angle β will also reflect at the sameangle. Thus to avoid the PD detecting specular light, it is offset. Thedegree of offset is dependent upon the height D2, the window openingwidth D1.

The substrate 70 supporting the window is made from black plastic and ischosen to be at a particular angle γ. If the plastic were constructed soas to have a horizontal roof (as denoted dashed line 60), light from theLED could bounce of the roof and onto the PD. To avoid this thesubstrate is angled such that light hitting the angled part reflectsdirectly back (as denoted by dashed line 62). Again this angle isdependent upon D1 and is approx 40% in the device shown by reference tothe solid line 64.

Finally the height of the divide is chosen to be a certain height suchthat light from the LED does not shine directly to the PD. The height ofthe divide will be determinant upon the height of the LED. In oneexemplary embodiment, the LED height is 1.5 mm and the divide height 2mm.

In a preferred embodiment the test strip comprises of a layer of aporous carrier such as nitrocellulose sandwiched between two layers ofplastic such as MYLAR®. The layer proximal to the light source must bepermeable to light, preferably transparent. In the situation wherein thePD's and LED are situated on the same side of the test-strip the layerdistal to the light source must be capable of reflecting light. It ispreferable for this distal layer to be white to increase contrast andhence the signal to noise ratio.

It is apparent that, in view of the inverse square law, it wouldgenerally be preferred to position the photodiodes as close as possibleto the test strip (i.e. decrease x), so as to increase the signalintensity I. However, merely decreasing the vertical separation ybetween the photodiode and the test strip would increase angle θ,decreasing the value of cos θ and therefore tend to reduce the signalintensity.

An alternative approach to improve signal intensity would be tore-position the photodiode nearer the center of the system, which wouldsimultaneously decrease the reflection distance and the angle ofreflection. However the distance must be minimized to ensure that themaximum intensity of light is detected (the intensity decreases as afunction of the distance of the PD from the test-strip and the angle ofreflection).

Example 10

In one exemplary embodiment, the active area of the photodetector is 2mm×2 mm. The light source provides light, at least some of which has awavelength of 635 nm. The height of the test-strip above the lightsource is 5.5 mm. The wall height separating the LED's is 2.7 mm and theangle of the wall is 30 degrees. The plastic used is black nylon.

Example 11

FIGS. 9-14 illustrate an exemplary embodiment of portions of an assayreader.

FIG. 9 shows an exploded view of a baffle arrangement 100 and a printedcircuit board (PCB) 102 that may receive the baffle arrangement. Thebaffle arrangement defines three windows 104 and includes a locationfeature 110 which may define an aperture 111 or some other feature thatcan engage a corresponding feature 112 on the PCB. The location feature110 may also be so sized and shaped as to engage a mating feature on atest strip (not shown) when the test strip is introduced to the bafflearrangement. The strip may thus be locked into position during an assaymeasurement. The baffle arrangement also includes parallel raised sidewalls 114 that may guide the test strip into the correct location andensure that it both engages with the location feature and is correctlylinearly aligned with the windows 104 and not skewed. The PCB includes,among other item not shown, light sources such as light emitting diodes(LED's) 106 and light detectors such as photodiodes (PD's) 108. TheLED's and PD's may be mounted in the same plane and positioned under therespective windows 104 such that light emitted from one or more LED's isable to pass through the window spaces onto the test-strip and bereflected back down onto one or more of the PD's.

FIG. 10 shows a top plan view of an exemplary embodiment of a bafflearrangement 110 in which the light source centers 106 a are alignedunder their respective windows 104.

FIG. 11 provides an underside view of baffle arrangement 100. Thearrangement may include a number of mounting pins 118 to provide contactpoints with the PCB (not shown). Defining windows 104 are baffles 116and side barriers 117 that have angled walls to screen light asdescribed above.

FIG. 12 shows a bottom plan view of the baffle arrangement 100. Thelight source centers 106 a are aligned under windows 104, and lightdetector centers 108 a are offset to provide the appropriate incidentangle, as described above.

FIG. 13 depicts a longitudinal cross-section (taken at line 10-10 inFIG. 7) of baffle arrangement 100 seated on PCB 102 and a test strip 120raised from its normal position in the baffle arrangement. The lightsources 106 are positioned in their respective windows 104.

FIG. 14 is a transverse cross section (taken at line 11-11 in FIG. 13)showing the test strip 120 in position relative to the bafflearrangement 100. The strip includes a porous carrier membrane 122 inwhich the assay reaction is conducted. Light emanative from a lightsource 106 impinges on the membrane. Light emanating from the membraneis detected by the light detector 108. A divider 124 prevents light fromsource 106 from shining directly on detector 108.

Example 12

An assay result reader according to the present disclosure may alsoinclude a system for declaring the result of an assay before completionof the assay, if a analyte measurement signal is above an upperthreshold or below a lower threshold. Such systems are described in U.S.patent application Ser. No. 10/741,416, filed Dec. 19, 2003.

Example 13

An assay result reader according to the present disclosure may alsoinclude a system for detecting flow rate of a fluid sample, such as onedescribed in U.S. patent application Ser. No. 10/742,459, filed Dec. 19,2003.

Example 14

An assay result reader according to the present disclosure may furtherinclude both an early declaration system described in U.S. patentapplication Ser. No. 10/741,416 and a flow rate detection systemdescribed in U.S. patent application Ser. No. 10/742,459.

Example 15

FIG. 15 is a graph showing the intensity of reflected light (arbitraryvalues) against time detected from each of the three zones, using asample which does not contain the analyte of interest. The profile forthe test zone is indicated by crosses, that for the reference zone bycircles, and that for the control zone by triangles.

Considering the test zone profile, there is an initial lag phase duringwhich the liquid sample is migrating along the porous carrier. In thisperiod, the level of light reflected by the test zone is essentiallyconstant. As the sample reached the test zone the amount of lightreflected sharply decreases. This is primarily due to absorption oflight by the coloured particulate label transported by the liquidsample. However some of the reduction in reflected light intensity issimply due to wetting of the nitrocellulose porous carrier, since drynitrocellulose is more reflective.

As the fluid front moves past the test zone the level of reflected lightstarts to increase, the coloured label being transported with the sampledownstream past the test zone. The reflected light intensity does notreturn to the original level because of the wetting of thenitrocellulose and because a small amount of the coloured particulatelabel is left behind as the liquid advances.

Generally similar profiles are exhibited by the reference and controlzones, although these are downstream of the test zone and so lag furtherbehind. The control zone profile, in particular, does not return to itsoriginal level of reflected light intensity because of development ofthe “control line” (i.e. deposition of coloured particulate label in thecontrol zone).

FIG. 16 is essentially similar, and shows the profiles obtained using %normalised results (i.e. test value divided by calibration value×100).The profile being expressed in terms of % of calibration value againsttime. FIG. 16 demonstrates that normalisation of the test readingsagainst an initial calibration reading reduces the variation in signalfrom the test, reference and control zones (although again the controlzone value remains low due to the deposition of labelled reagent in thecontrol zone).

In order to calculate the flow rate of the liquid sample along theporous carrier, the exemplified reading device actually compares thenormalised results from the test and control zones with the resultobtained from the reference zone in order to arrive at a “Relativeattenuation of reflected light intensity” (% A).

$\left\lbrack {{\% \mspace{14mu} A} = \frac{\left( {{{{Ref}(t)}/{{Ref}({cal})}} - {{{Test}(t)}/{{Test}({cal})}}} \right.}{{{Ref}(t)}/{{Ref}({cal})}}} \right\rbrack$

Typical % A profiles (against time), for a sample containing a relevantanalyte of interest, are shown in FIG. 17. A positive attenuation meansthat the zone in question is reflecting less light than the referencezone, whilst a negative attenuation means that the zone in question isreflecting more light than the reference zone.

Referring to the % A profile of the test zone, it is apparent that thetest zone signal is initially greatly attenuated (relative to thereference zone) when the liquid sample (with coloured particulate label)reached the test zone, but has not yet reached the reference zone. Afterabout 35 seconds, the liquid sample starts to reach the reference zoneand this leads to a sudden drop in the relative attenuation of the testzone. After about 40 seconds, the fluid front starts to leave thereference zone leading to an increase in the reflectivity of thereference zone and therefore an increase in the relative attenuation ofthe test zone. This levels off and eventually reaches a plateau, at apositive attenuation of just under 30%, the test zone having capturedsome of the coloured particulate label due to the presence in the sampleof the analyte of interest.

Considering the profile for the control zone, it is apparent that thereis an initial sharp fall (negative attenuation), since the liquid samplereaches the reference zone before the control zone. As the liquid samplestarts to leave the reference zone before the control zone the relativenegative attenuation in signal from the control zone starts to return tozero, and as the liquid samples reached the control zone the relativeattenuation becomes positive and reached a plateau level of about 15%,due to the deposition of labelled reagent in the control zone to providea positive control result.

Whilst in the presently exemplified reader the test zone result iscompared with the reference zone result, a useful alternative would beto compare the test zone result with the control zone result.

In general terms the flow rate is calculated by detecting the change inreflected light intensity associated with the arrival of the liquidsample at a particular zone, and determining the time which elapsesbetween the arrival of the liquid sample at the various zones. Moreprecisely, the flow rate is calculated as described below.

The signal at all three zones is measured irrespective of the positionof liquid on the test strip.

The signal attenuation at the test zone is measured with respect thesignal attenuation at the reference zone. When the fluid front arrivesat the test zone the signal attenuation will change relative to thereference zone, due to the fluid front not yet having reached thereference zone (it being positioned downstream from the test zone).Timing is commenced when the signal attenuation of the test zonerelative to the reference zone is greater than 10%. It should bementioned that the value of 10% indicates the degree of confidenceincluding any margin of error which has been attached to the measurementreading, which in itself depends on the various measurement parameters,e.g. test strip, optics. This might vary and be chosen to be anyconvenient value.

The liquid then proceeds into the reference zone and when the signalattenuation of the control zone relative to the reference zone isgreater than minus 10% (−10%), the device considers that the liquid hasreached the control zone (the minus value reflecting that the controlzone is positioned downstream from the test zone). When the signalattenuation of the control zone relative to the reference zone isgreater (i.e. more positive) than zero, the device determines that theliquid has reached the control zone. Thus the time measurement by thedevice may not necessarily exactly correspond to the time when the fluidarrives at the respective zones.

Although in this example the reader measures the rate of passage ofliquid between the test and control zones, it measures it with respectto the signal obtained from the reference zone. However the arrival ofliquid at the test and control zones could be determined absolutely,(i.e. not by measurement with respect to the reference zone).

The reader is also programmed to declare an assay result invalid if theliquid sample is detected at the control zone before it is detected atthe reference zone, as this is indicative that the liquid sample hasfollowed an abnormal flow path.

Example 16

A single set of optics is used to determine both the signal and the flowrate. The maximum and minimum flow rates are set at 5 and 40 s,respectively. Thus any sample that takes longer than 40 s is rejected asbeing too slow (which may be due to undersampling), any sample that isquicker than 5 s is rejected as being too fast. The flow rate will beinfluenced by a number of factors including porosity, distance betweencontrol and test-lines as well as any chemistry in the porous stripwhich might modify flow.

Timing is determined and set to zero when the fluid reaches thetest-line. The timer is then set and the time for the fluid to reach thecontrol line is measured. As a further control check, the devicemonitors that the fluid has passed through the reference zone.Additionally as a further control feature, the device also monitors thatthe fluid has passed through the test, reference and control zones inthat order before it will accept a flow rate measurement as authentic,even if it satisfies the flow rate range of between 5 and 40 s.

In other embodiments, of course, the upper and lower flow rate limitscan be set to a wide variety of values, in accordance with particularproperties of test fluids and/or with the factors described above.

Example 17

An assay result reader according to the present disclosure may alsoinclude a system for declaring the result of an assay before completionof the assay, if a analyte measurement signal is above an upperthreshold or below a lower threshold. Such systems are described in U.S.patent application Ser. No. 10/741,416, filed Dec. 19, 2003, attorneydocket number ISA-006.01.

Example 18

An assay result reader according to the present disclosure may alsoinclude optical arrangement such as those described in U.S. PatentApplication Ser. No. 60/508,001, filed Oct. 2, 2003.

All patents and patent applications referred to in this disclosure arehereby incorporated herein in their entireties by this reference.

1. A device for determining an assay result, comprising: a test stripcomprising at least a first zone and a second zone spaced apart from oneanother along a flow path defined by the test strip; a light sourcesystem configured to illuminate the first zone and the second zone ofthe test strip; a light detection system configured to detect light fromat least one of the zones when the respective zone is illuminated by thelight source and output a signal indicative of an amount of an analyteor rate of accumulation of analyte in that zone; and a processorconfigured to receive the signal, compare the signal to a threshold, andgenerate an output signal if the signal exceeds the threshold, theoutput signal indicative of a positive result if the signal exceeds thethreshold.
 2. An assay result reading device for reading the result ofan assay to detect the presence and/or amount of an analyte of interestand wherein the presence or absence, as appropriate, of the analyte ofinterest causes a reaction which leads to the accumulation of a signalin a time dependent manner, the device comprising: means for determiningthe rate or amount of signal accumulation; means for comparing thedetermined rate or amount of signal accumulation with an upper thresholdvalue; and means for declaring the result of the assay if the determinedrate or amount of signal accumulation exceeds the upper threshold valuebefore the assay has been completed.
 3. A method comprising: performingan assay; before the assay has reached equilibrium, generating a signalrepresenting the amount of an analyte or the rate of accumulation of ananalyte; comparing the signal with a first threshold value; anddeclaring a result of the assay if the determined rate or amount ofsignal accumulation exceeds the first threshold value.
 4. An assayresult reading device for reading the result of an assay to detect thepresence and/or amount of an analyte of interest and wherein thepresence of the analyte of interest causes a reaction which leads to theaccumulation of a signal in a time dependent manner, the devicecomprising: means for determining the rate or amount of signalaccumulation; means for comparing the determined rate or amount ofsignal accumulation with threshold value; and means for declaring theresult of the assay if the determined rate or amount of signalaccumulation exceeds the threshold value.
 5. A device for determining anassay result comprising; a. a test strip, b. a light source system, c. alight detection system, d. a processor and/or a computation circuitconfigured to be responsive to a signal representing the amount of ananalyte or the rate of accumulation of an analyte before the assayreaches equilibrium and to compare the signal to an upper threshold andto generate an output signal if the signal exceeds the upper threshold,the output signal indicative of a positive test result if the signalexceeds the upper threshold. e. a display, wherein the device displaysan early result if analyte accumulation or rate of accumulation exceedsthe upper threshold.